package juc.lock;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

class MyCache
{
    private volatile Map<String,Object> map = new HashMap<>();
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    /**
     * 写数据
     * @param key
     * @param value
     */
    public void put(String key,Object value) {
        readWriteLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 写入数据" + key);
            //暂停一会
            try { TimeUnit.MILLISECONDS.sleep(300); } catch (InterruptedException e) { e.printStackTrace(); }

            map.put(key,value);
            System.out.println(Thread.currentThread().getName() + "\t 写入完成");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.writeLock().unlock();
        }

    }

    /**
     * 读数据
     * @param key
     */
    public void get(String key) {
        readWriteLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 读取数据");
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName() + "\t 读取完成" + result);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.readLock().unlock();
        }

    }

}

/**
 * @author Guo
 * @Create 2020/9/1 16:55
 * 多个线程同时读一个资源类没有任何问题，所以为了满足并发量，读取共享资源可以同时进行
 * 但是
 * 如果有一个线程想去写共享资源类，就不应该再有其他线程可以对资源进行读或写
 * 小总结:
 *      读-读能共享
 *      读-写不能共享
 *      写-写不能共享
 */
public class ReadWriteLockDemo {
    public static void main(String[] args) {
        MyCache cache = new MyCache();

        for(int i = 1; i <= 5; i++) {
            final int tempInt = i;
            new Thread(() -> {
                cache.put(tempInt + "",tempInt+"");
            },String.valueOf(i)).start();
        }
        for(int i = 1; i <= 5; i++) {
            final int tempInt = i;
            new Thread(() -> {
                cache.get(tempInt + "");
            },String.valueOf(i)).start();
        }
    }
}